Field of the Invention
The present invention relates to a Group III nitride semiconductor light-emitting device, more specifically, the one characterized by the structure of a light-emitting layer.
Background Art
In the Group III nitride semiconductor light-emitting device, a MQW structure in which a well layer and a barrier layer are repeatedly deposited is widely used as a light-emitting layer. The well layers are formed of InGaN and have the same In composition ratio.
Japanese Patent No. 3433038 describes that the In composition ratios of a well layer closest to an n-type cladding layer and a well layer closest to a p-type cladding layer are reduced than the In composition ratio of a well layer at the center, thereby relaxing the strain applied from both the n-type cladding layer and the p-type cladding layer to a light-emitting layer.
Japanese Patent Application Laid-Open (kokai) No. 2014-110396 describes that an nESD layer (n-side electrostatic breakdown preventing layer) is formed between an n-type contact layer and an n-type cladding layer, thereby generating pits in the nESD layer. The pits pass through the well layer and reach a surface of the p-type contact layer. Generation of such pits relaxes the strain in a light-emitting layer, thereby improving the emission efficiency.
However, in the method described in Japanese Patent No. 3433038, the In concentrations of the well layers closest to the n-type cladding layer and the p-type cladding layer respectively are reduced. These well layers cannot emit light, and the emission efficiency might be reduced.
Although the strain can be reduced by generating pits as described in Japanese Patent Application Laid-Open (kokai) No. 2014-110396, the strain is not sufficiently eliminated, and further strain relaxation was required.